Electric furnace and method of producing molten magnetite therein.



A. P. SCOTT.

E LECTRIC FURNACE AND METHUD 0F PRODUCING MOLTEN MAGNETITE THEHEIN.

vAPPLICATION FILED NDV.` 17.19l5.

Patented May15,r1917.

IN VEN TOR A TTORNEYS ARTHUR P. SCOTT, OF CHICAGO, ILLINOIS, ASSIGNOR ToCHILE ExrLonArIoN com- .'PANY, 0F NEW YORK, N. Y., A CORPORATION O F NEWJERSEY.

ELECTRIC FUBNACE AND METHOD OF PRODUCING MOLTEN MAGNETITE THEBEIN.

Specioation of Letters Patent.

Patented May 15, 191'?.

Application led November 17, 1915. Serial No. 61,905.

To all whom z't may concern.'

Be it known that I, ARTHUR P. Soo'rr, a subject ofthe King of GreatBritain, residing at Chicago, county of Cook= and State of Illinois,have invented certain new and useful Improvements in Electric Furnacesand Methods ,of Producing Molten Magnetite Therein; and I do herebydeclare the following to be a full, clear, and exact description of theinvention, such as will enable others skilled in the art to which itappertains to make and use the same. l

This invention relates to improvements in single phase alternatingcurrent electric furnaces of the direct are type, and particularly tofurnaces for the melting of iron ore and the production of moltenmagnetite therefrom; and to methods of producing a protective layer ofmagnetite, and molten magnetite, therein.

In furnaces of this type, whenI utilized for melting ore, (purple ore orleached Rio Tinto cinder), it has been found that the arc tends to meltprincipally downward and with very little lateral fusion, and that thebath thus tends to assume the form of a deep well of small cross sectioninstead of the usual shallow basin. Inorder toprotect the bottom contactfrom overheating and injury during this melting process, the *furnacebottom is provided, according'to the present invention, lwith aprotective layer of solid magnetite above the bottom contact. While theore itself is a non-conductor, it

becomes a good conductor when molten andV cast, so that the protectivelayer itself forms the bottom electrode.

A furnace embodying the invention and illustrative thereof is shown inthe .accompanylng drawings in central vertical sectlon.

The furnace illustrated is of lthe tilting type and is providedwithsuitable means (not shown) for rocking or tilting it into theposition shown in dotted lines. The furnace is constructed ofappropriate refractory materiali within an outer casing and is providedwith a top 2, and bottomrocker supports 8 mounted upon the foundation 4.

The upper graphite electrode is indicated at 5, carriedby an arm 6. Thisarm is adjustable in the vertical support 7 by means of suitableadjusting or operating mechanism 8. The bottom contact is indicated at10 and the lateral opening in the furnace, by means of which access to,at 1l. Above the bottom steel contact, and formmg a bottom protectivelayer, is the cast layer ofmagnetite 9. v

In the production of. molten is essential that the furnace lining be ofa basic nature. In practice this lining is made of magnesite. A mixtureof the magnesite with pitchis tamped into the shell around a woodenform. After removing the form, the pitch is removed,'as by a slow cokefire, and the furnace is ready for operation.

In starting the furnace and producing the layer of magnetite, the ore(e. g. purple ore or leached Rio Tinto cinder) in suitableamount ispiled up around the sides of the hearth to allow the upper graphiteelectrode to pass through and make contact with the bottom steelelectrode. This is necessary because of the non-conducting character ofthe raw ore. After the electric current has been turned on, the upper'graphite electrode is lowered into contact with the bottom to make thearc and-then gradually raised.

As fast as the material below the arc is melted, fresh ore is rabbleddown from the sides with a Wooden pole to prevent the bottom contactfrombeing eaten away b the molten magnetite. As soon as a su cientquantity of pasty material has accumulated below rabbling is stopped andthe current left. on for five or ten minutes to allow the melt to becomefluid and clear. cut oil and the furnace allowed to cool for arsuitableperiod of time g. three or four hours) to permit the bottom to set. Theoperation is repeated until the magnetite bot.-

may be had theremagnetite ity The current is thenl the arc (e. gfabouthalf an hour), the l tom has attained a suiiicient thickness for use inthe normal melting operation, and the furnace is then allowed to remaininactive for a further period of time, say over night. f

Because of the tendency of the arc to melt principally downward, andwith little lateral fusion, and of the-resultin tendency of the bath toassume the form o a deep well of small cross section instead of theusual shallow basin, it has been found that the magnetite bottomimmediately below the electrode was frequently penetrated, making itnecessary to suspend o erations or even to build up an entire newAottom.

It has been found, however, that this diiiculty can be readily overcomeby the addition of broken magnetite electrode scrap. This scrap, whenadded to the bath, is but slowly absorbed, the raw ore going intosolution, or becoming molten, much more readily. This scrap settles tothe bottom of the bath, and where raw ore is added from time to timeremains practically unattacked.

Accordingly, when the magnetite bottom has become penetrated and needsrepairing, or to prevent danger-:of such penetra-tion,

the magnetite scrap is added. It .may thus form a layer at the bottom ofthe molten ore and above the protective laver of'magnetite, `or it maybeor become 'incorporated in this protective layer itself.

The roof of the furnace can be made of.

basic material, or even of silica brick, the silica remainingpractically unaffected. It tends to.sla with the"'ore whenthe latter isaccidenta y brought into contact. with it,-

but as this can readily be avoided the'tend enc isvnegligiblel A fterthe protective layer of magnetite has been formed the furnace Vis readyfor use inthe normal operation of melting the ore for the production ofmagnetite suitable for casting purposes, 4e.' g. for casting electrodes.

.In the normalv meltm operation, the graphite electrode Vis first oweredinto contact with themagnetite bottom, a suitable charge of the ore isVthrown in around the electrode, and the electrode gradually raised asfast as the ore near the arc is melted and becomes conducting. At thesame time the i bath of suiiicient outlying portions of the chargearound the periphery of the hearth are gradually poled down into thezone of4 fusion. When the bath has become .clear and fluid and of a proer temperature, it is ready for pourin efore pouring, and after theclear uigd guantity has accumulated, lit is -in practice a vantageous toadd a further small portion of the ore and to pour the molten ore assoon as this added portion has been absorbed. This final addition servesboth as a temperature check and to limit the formation of an excess offerrous oxid. The temperature of the ore when cast is about 1590 C.

The method of casting the electrodos after a suitable bath has beenproduced forms the subject-matter of a companion application, Serial No.61,904, filed November 17, 1915. lFrom the above description it will beseen that the magnetite bottom not only protects the magnesite liningfrom the dlrect heat of the arc, but it takes the place of the steelbottom contact preventin excessive corrosion at this point and itse fforming the lower electrode. It will further be seen that by the simpleexpedient of adding cast magnetite electrode scrap to the bath, orincorporating it in the bottom protective layer, the magnetite layer isitself preserved and protected from overheating and penetration. I

What I claim is:

1. An electric furnace of the direct arc type provided with a bottomprotective conducting layer of mhgnetite; substantially as described.

'2. An electric furnace of the direct are type provided with a lower xedcontact and an upper movable electrode, and with a protective conductinglayer of magnet-ite overlying said bottom contact and forming the bottomelectrode; substantially as described.

3. An electric furnace of the direct `arc type provided with a bottomprotective conducting layer of magnetite with which cast magnetite scrapis incorporated; substanti ally as described.

4.-- An electric furnace of the direct arc type provided. with a lowerfixed contact and an upper movable electrode, and with a protectiveconducting layer of magnetite Aoverlying said bottom contact and forminglthe bottom electrode, said layer of. magnetite having cast magneti-tescrap incorporated therewith.; substantially as described.

-5. A single phase alternating current electric furnace ofthe direct arctype provided with aflower fixed electrode and an upper movableelectrode, and with a protectivevconducting layer of magnetite overlyingelectric'arc furnace to produce a duid body of the magnetite, allowinglsaid body to set to form a bottom protective layer, and pro tecting thebottom contact by such protective layer during the subsequent melting offurther portions of ore; substantially as described. y n

'8. In a method of producing molten magnetite, melting the ore betweenthe up er and lower electrodes of an electric arc urnace'to produce afluid bodyr of magnetite,' allowing such body to set, and melting fur.

ther amount of ore above said protective l layer of magnetite to producefurther amounts of fluid magnetite, and permitting said further amountsof magnetite to 'set to form a" bottom protective layer of suitablethickness substantially as described.

ture. 4

ARTHUR P. SCOTT.

In testlmony whereof I aix my signan

